1. Field of the Invention
The present invention relates to a synchronous motor control device for correcting a deviation in rotational position of a synchronous motor, and also to a method of correcting the deviation in rotational position of the synchronous motor using the control device.
2. Description of the Related Art
A conventional method of correcting a deviation caused between a motor rotational position determined from an output of a rotational position detector and an actual motor rotational position includes: a step of detecting a no-load state of a motor by an unloading detector; a step of detecting a motor voltage applied to the windings of a motor by a motor voltage detector; a step of computing d-axis and q-axis voltages from rotational angular information of the rotational position detector and the motor voltage; and a step of correcting a rotational angle such that the d-axis voltage becomes zero (for example, see JP 06-165561 A).
Also, another method includes: a step of supplying predetermined DC currents to coils of a three-phase synchronous motor; a step of detecting a rotational position of the three-phase synchronous motor stopped at a theoretical rotational position by supplying the predetermined currents; a step of determining as a correction value a deviation between the detected rotational position of the motor and a preset theoretical rotational position; and a step of correcting the detected rotational position of the motor based on the correction value (for example, see JP 2001-128484 A).
Further, another method includes: a step of setting an instruction torque current as zero and inputting an instruction magnetic flux current of an arbitrary finite repetition waveform to a motor; a step of computing an angular acceleration from a detection rate; a step of estimating a torque produced from a motor from the instruction magnetic flux current, the angular acceleration, inertia of the motor, viscous friction of the motor, and friction torque of the motor using a motor motion equation; a step of estimating a torque current by dividing the estimated torque by a torque constant of the motor; a step of estimating a magnetic flux current using the instruction magnetic flux current and the estimated torque current; and a step of estimating an initial magnetic polar position using the estimated magnetic flux current and the estimated torque current (for example, see JP 2001-204190 A).
In the case of using the conventional method of correcting the deviation caused between the rotational position of the synchronous motor which is determined from the output of the rotational position detector and the actual rotational position of the synchronous motor, it is necessary to provide the motor voltage detector and the unloading detector. Therefore, an apparatus to which this method is applied becomes expensive.
Also, in the conventional method, it is expected to stop a rotor at a predetermined position by supplying a DC current. Therefore, in a state in which a load such as an internal combustion engine is connected with the rotor, there is a fear that the rotor stops at a position deviated from the predetermined position by the frictional force of the load, so that the deviation in rotational position cannot be precisely corrected.
Also, in the conventional method, the torque current Iq is set as zero and the amount of deviation in rotational position is estimated from a change in rotational rate when a magnetizing current Id is changed. Therefore, when the load is connected with the rotor, the precise position correction cannot be performed because of a variation in rotational rate resulting from the load.